The present invention relates to secure messaging systems.
Communication networks in which a considerable number of terminals such as personal computers are interconnected are well known. Such systems often use communication media which are not secure, such as public telephone systems, in that they are liable to passive interference (eavesdropping) and active interference (interception and removal of messages, modification of messages, and insertion of false messages). To overcome these problems, it is known to provide encryption systems. However, while the principle of encryption is obvious, there are considerable practical problems involved in designing a system which includes a substantial number of terminals.